Flat-top optical resonance in a single-ring resonator based on manipulation of fast- and slow-light effects

Optical single-ring resonance inherently generates Lorentzian-shape magnitude and group-delay responses, leading to critical performance limitation in photonics, cavity quantum electrodynamics, cavity optomechanics, and atomic and optical physics. Here, we propose a new type of microresonator that stimulates flat-top resonance in a single-ring cavity. By manipulating the fast and slow light effects in the microresonator, the flat-top group delay can be tuned with an ignorable magnitude variation. In addition, the bandpass response can be switched to a notch, which can enable function-reconfigurable photonic integrated circuits (PICs) without a physical change in the architecture. Our demonstration provides the possibility of developing microresonator-based PICs with unprecedented high flexibility and capacity.